As Ted Cruz worked the crowd at Indiana’s Republican Party spring dinner last week, his father was traveling to Puerto Rico on his behalf on a mission that could help determine whether or not the Texas lawmaker wins the Republican nomination.

The firebrand senator asked his father, Rafael Cruz, to head to the U.S. territory, the Washington Post reports, to meet privately with Puerto Rico’s 23 delegates, all of whom are pledged to vote at the Republican National Convention for a candidate who is not even in the race anymore.

Florida Sen. Marco Rubio won the Puerto Rican GOP primary in early March. So far, Rubio – who dropped out of the race following a demoralizing loss in his home state of Florida on March 15 – has done what he can to hang to those 23 delegates and the 148 others he won caucuses and primaries across the country.

Rubio sent letters to all the state parties where he won delegates, advising them that the suspension of his campaign should not be interpreted as giving up his delegates. Whether or not they remain bound to him at the convention is up to individual state rules, and estimates have the Florida lawmaker pulling in at least 50 delegates on the first ballot in Cleveland.

So why father Cruz meeting with the delegates?

Because if GOP front-runner Donald Trump does not secure the 1,237 delegates that he needs to take the nomination on the first ballot, the delegates promised to Rubio are up for grabs, and his son would love to have them join his camp.

This sort of second-ballot maneuvering gives Cruz his only hope of winning the nomination – something that is mathematically out of his grasp in a first ballot after big losses in Tuesday night’s primaries – but it also gives Puerto Rican delegates a lot of leverage.

“Whoever wants our vote needs to pay attention to our particular issues, as well as our struggle for equality as U.S. citizens. If that’s not taken into consideration, we could care less what the polls say,” said San Juan attorney Elias Sánchez, a delegate who also co-chaired Rubio’s Puerto Rico campaign.

Rubio seemed a good fit to many Puerto Rican Republican voters as he supported statehood for the territory. Cruz has come out only in support of Puerto Rico’s “right of self-determination,” as has Trump, something the delegates say is not enough.

Delegates told the Post that Rafael Cruz’s trip to the island was appreciated, but there’s no guarantee his son will win their vote if the convention goes to a second ballot. What the delegates are willing to commit to is to vote in a bloc, however many ballots are needed to nominate a candidate.